/*
 *  sha1.c
 *
 *  Description:
 *      This file implements the Secure Hashing Algorithm 1 as
 *      defined in FIPS PUB 180-1 published April 17, 1995.
 *
 *      The SHA-1, produces a 160-bit message digest for a given
 *      data stream.  It should take about 2**n steps to find a
 *      message with the same digest as a given message and
 *      2**(n/2) to find any two messages with the same digest,
 *      when n is the digest size in bits.  Therefore, this
 *      algorithm can serve as a means of providing a
 *      "fingerprint" for a message.
 *
 *  Portability Issues:
 *      SHA-1 is defined in terms of 32-bit "words".  This code
 *      uses <stdint.h> (included via "sha1.h" to define 32 and 8
 *      bit unsigned integer types.  If your C compiler does not
 *      support 32 bit unsigned integers, this code is not
 *      appropriate.
 *
 *  Caveats:
 *      SHA-1 is designed to work with messages less than 2^64 bits
 *      long.  Although SHA-1 allows a message digest to be generated
 *      for messages of any number of bits less than 2^64, this
 *      implementation only works with messages with a length that is
 *      a multiple of the size of an 8-bit character.
 *
 */

#include "sha1.h"

/*
 *  Define the SHA1 circular left shift macro
 */
#define SHA1CircularShift(bits,word) \
                (((word) << (bits)) | ((word) >> (32-(bits))))

/* Local Function Prototyptes */
void SHA1PadMessage(SHA1Context *);
void SHA1ProcessMessageBlock(SHA1Context *);

/*
 *  SHA1Reset
 *
 *  Description:
 *      This function will initialize the SHA1Context in preparation
 *      for computing a new SHA1 message digest.
 *
 *  Parameters:
 *      context: [in/out]
 *          The context to reset.
 *
 *  Returns:
 *      sha Error Code.
 *
 */
int SHA1Reset(SHA1Context *context)
{
	if (!context)
	{
		return shaNull;
	}

	context->Length_Low = 0;
	context->Length_High = 0;
	context->Message_Block_Index = 0;

	context->Intermediate_Hash[0] = 0x67452301;
	context->Intermediate_Hash[1] = 0xEFCDAB89;
	context->Intermediate_Hash[2] = 0x98BADCFE;
	context->Intermediate_Hash[3] = 0x10325476;
	context->Intermediate_Hash[4] = 0xC3D2E1F0;

	context->Computed = 0;
	context->Corrupted = 0;
	return shaSuccess;
}

/*
 *  SHA1Result
 *
 *  Description:
 *      This function will return the 160-bit message digest into the
 *      Message_Digest array  provided by the caller.
 *      NOTE: The first octet of hash is stored in the 0th element,
 *            the last octet of hash in the 19th element.
 *
 *  Parameters:
 *      context: [in/out]
 *          The context to use to calculate the SHA-1 hash.
 *      Message_Digest: [out]
 *          Where the digest is returned.
 *
 *  Returns:
 *      sha Error Code.
 *
 */
int SHA1Result(SHA1Context *context,
	uint8_t Message_Digest[SHA1HashSize])
{
	int i;

	if (!context || !Message_Digest)
	{
		return shaNull;
	}

	if (context->Corrupted)
	{
		return context->Corrupted;
	}

	if (!context->Computed)
	{
		SHA1PadMessage(context);
		for (i = 0; i<64; ++i)
		{
			/* message may be sensitive, clear it out */
			context->Message_Block[i] = 0;
		}
		context->Length_Low = 0;    /* and clear length */
		context->Length_High = 0;
		context->Computed = 1;
	}

	for (i = 0; i < SHA1HashSize; ++i)
	{
		Message_Digest[i] = context->Intermediate_Hash[i >> 2]
			>> 8 * (3 - (i & 0x03));
	}

	return shaSuccess;
}

/*
 *  SHA1Input
 *
 *  Description:
 *      This function accepts an array of octets as the next portion
 *      of the message.
 *
 *  Parameters:
 *      context: [in/out]
 *          The SHA context to update
 *      message_array: [in]
 *          An array of characters representing the next portion of
 *          the message.
 *      length: [in]
 *          The length of the message in message_array
 *
 *  Returns:
 *      sha Error Code.
 *
 */
int SHA1Input(SHA1Context    *context,
	const uint8_t  *message_array,
	unsigned int length)
{
	if (!length)
	{
		return shaSuccess;
	}

	if (!context || !message_array)
	{
		return shaNull;
	}

	if (context->Computed)
	{
		context->Corrupted = shaStateError;
		return shaStateError;
	}

	if (context->Corrupted)
	{
		return context->Corrupted;
	}
	while (length-- && !context->Corrupted)
	{
		context->Message_Block[context->Message_Block_Index++] =
			(*message_array & 0xFF);

		context->Length_Low += 8;
		if (context->Length_Low == 0)
		{
			context->Length_High++;
			if (context->Length_High == 0)
			{
				/* Message is too long */
				context->Corrupted = 1;
			}
		}

		if (context->Message_Block_Index == 64)
		{
			SHA1ProcessMessageBlock(context);
		}

		message_array++;
	}

	return shaSuccess;
}

/*
 *  SHA1ProcessMessageBlock
 *
 *  Description:
 *      This function will process the next 512 bits of the message
 *      stored in the Message_Block array.
 *
 *  Parameters:
 *      None.
 *
 *  Returns:
 *      Nothing.
 *
 *  Comments:
 *      Many of the variable names in this code, especially the
 *      single character names, were used because those were the
 *      names used in the publication.
 *
 *
 */
void SHA1ProcessMessageBlock(SHA1Context *context)
{
	const uint32_t K[] = {       /* Constants defined in SHA-1   */
		0x5A827999,
		0x6ED9EBA1,
		0x8F1BBCDC,
		0xCA62C1D6
	};
	int           t;                 /* Loop counter                */
	uint32_t      temp;              /* Temporary word value        */
	uint32_t      W[80];             /* Word sequence               */
	uint32_t      A, B, C, D, E;     /* Word buffers                */

	/*
	 *  Initialize the first 16 words in the array W
	 */
	for (t = 0; t < 16; t++)
	{
		W[t] = context->Message_Block[t * 4] << 24;
		W[t] |= context->Message_Block[t * 4 + 1] << 16;
		W[t] |= context->Message_Block[t * 4 + 2] << 8;
		W[t] |= context->Message_Block[t * 4 + 3];
	}

	for (t = 16; t < 80; t++)
	{
		W[t] = SHA1CircularShift(1, W[t - 3] ^ W[t - 8] ^ W[t - 14] ^ W[t - 16]);
	}

	A = context->Intermediate_Hash[0];
	B = context->Intermediate_Hash[1];
	C = context->Intermediate_Hash[2];
	D = context->Intermediate_Hash[3];
	E = context->Intermediate_Hash[4];

	for (t = 0; t < 20; t++)
	{
		temp = SHA1CircularShift(5, A) +
			((B & C) | ((~B) & D)) + E + W[t] + K[0];
		E = D;
		D = C;
		C = SHA1CircularShift(30, B);
		B = A;
		A = temp;
	}

	for (t = 20; t < 40; t++)
	{
		temp = SHA1CircularShift(5, A) + (B ^ C ^ D) + E + W[t] + K[1];
		E = D;
		D = C;
		C = SHA1CircularShift(30, B);
		B = A;
		A = temp;
	}

	for (t = 40; t < 60; t++)
	{
		temp = SHA1CircularShift(5, A) +
			((B & C) | (B & D) | (C & D)) + E + W[t] + K[2];
		E = D;
		D = C;
		C = SHA1CircularShift(30, B);
		B = A;
		A = temp;
	}

	for (t = 60; t < 80; t++)
	{
		temp = SHA1CircularShift(5, A) + (B ^ C ^ D) + E + W[t] + K[3];
		E = D;
		D = C;
		C = SHA1CircularShift(30, B);
		B = A;
		A = temp;
	}

	context->Intermediate_Hash[0] += A;
	context->Intermediate_Hash[1] += B;
	context->Intermediate_Hash[2] += C;
	context->Intermediate_Hash[3] += D;
	context->Intermediate_Hash[4] += E;

	context->Message_Block_Index = 0;
}


/*
 *  SHA1PadMessage
 *
 *  Description:
 *      According to the standard, the message must be padded to an even
 *      512 bits.  The first padding bit must be a '1'.  The last 64
 *      bits represent the length of the original message.  All bits in
 *      between should be 0.  This function will pad the message
 *      according to those rules by filling the Message_Block array
 *      accordingly.  It will also call the ProcessMessageBlock function
 *      provided appropriately.  When it returns, it can be assumed that
 *      the message digest has been computed.
 *
 *  Parameters:
 *      context: [in/out]
 *          The context to pad
 *      ProcessMessageBlock: [in]
 *          The appropriate SHA*ProcessMessageBlock function
 *  Returns:
 *      Nothing.
 *
 */

void SHA1PadMessage(SHA1Context *context)
{
	/*
	 *  Check to see if the current message block is too small to hold
	 *  the initial padding bits and length.  If so, we will pad the
	 *  block, process it, and then continue padding into a second
	 *  block.
	 */
	if (context->Message_Block_Index > 55)
	{
		context->Message_Block[context->Message_Block_Index++] = 0x80;
		while (context->Message_Block_Index < 64)
		{
			context->Message_Block[context->Message_Block_Index++] = 0;
		}

		SHA1ProcessMessageBlock(context);

		while (context->Message_Block_Index < 56)
		{
			context->Message_Block[context->Message_Block_Index++] = 0;
		}
	}
	else
	{
		context->Message_Block[context->Message_Block_Index++] = 0x80;
		while (context->Message_Block_Index < 56)
		{
			context->Message_Block[context->Message_Block_Index++] = 0;
		}
	}

	/*
	 *  Store the message length as the last 8 octets
	 */
	context->Message_Block[56] = context->Length_High >> 24;
	context->Message_Block[57] = context->Length_High >> 16;
	context->Message_Block[58] = context->Length_High >> 8;
	context->Message_Block[59] = context->Length_High;
	context->Message_Block[60] = context->Length_Low >> 24;
	context->Message_Block[61] = context->Length_Low >> 16;
	context->Message_Block[62] = context->Length_Low >> 8;
	context->Message_Block[63] = context->Length_Low;

	SHA1ProcessMessageBlock(context);
}

int SHA1(const uint8_t *message, unsigned int length, uint8_t digest[SHA1HashSize])
{
	SHA1Context sha;
	int err;
	err = SHA1Reset(&sha);
	if (err) return err;
	err = SHA1Input(&sha, message, length);
	if (err) return err;
	err = SHA1Result(&sha, digest);
	if (err) return err;
	return shaSuccess;
}
